Displacement sensors, such as microphones and pressure sensors, are well-known in the prior art. Displacement sensors based on capacitive, impedance, and optical measurements have been developed. Optical displacement sensors are particularly attractive because they overcome many of the limitations of capacitive and impedance measurement techniques, such as low sensitivity, the need for high-voltage biasing, poor electrical isolation, or response nonlinearities.
Optical-displacement sensors known in the prior art operate by detecting light that is reflected and/or transmitted by an optical element that changes its reflectivity and/or transmissivity in response to an environmental stimulus, such as pressure differential, sound, vibration, etc. The detected light is converted into an electrical signal. This signal is a function of the reflectivity and/or transmissivity of the optical element, and, therefore, a function of the stimulus as well.
It can be advantageous to detect the light that is both reflected and transmitted from the optical element. For example, a differential signal based on the optical energy in the two beams can reduce the negative impact of source noise, shot noise, etc., on the output signal. Prior art approaches tend to be complex and costly to implement, however.
An optical displacement sensor that generates an output with reduced cost and complexity would, therefore, be a significant advance in the art.